How do I prevent the app from reloading the forecast each time it's opened?

First you want to make sure you are leaving the app using the home button and not the back button. If you use the back button the app will close completely, but with the home button it will only be suspended. You will also need to disable auto updating in the app settings. Press the menu button, select settings, then general. Change the update interval to manual.

How do I get into the app settings?

You can get to the app settings by pressing the menu button. If your phone or tablet doesn't have a menu button, Android will show 3 vertical dots at the bottom of the screen which you can press to bring up the menu. If you don't have a menu button or the 3 dots, that means your device does have a menu button but it is hidden. Often this means you have to hold down (or long press) on a different button to bring up the menu. For example, on the Galaxy S5 you have to hold down the recents button. On other devices you have to hold down the home button. If you still can't find the menu button, check your manual or look online for how to access it.

What is the difference between the free and paid versions?

The free version displays ads and has a limit of 3 saved locations. The paid version has no ads and no restrictions.